The Sevier Fold and Thrust Belt in Idaho: Road Log Geology

By Mr. William A. Szary M.S.

The segment of the Sevier-Laramide fold thrust belt exposed in southeastern Idaho was thrust farther toward the interior of North America than other parts of the thrust belt and as such is called a "salient". In southeastern Idaho, northeastern Utah, and western Wyoming, this is called the Wyoming salient and it has been extensively studied. Folding and thrust faulting occurred here during the Cretaceous to Paleocene Sevier orogeny (140 to 55 Ma). The Sevier orogeny was a time of active horizontal shortening and vertical thickening of the crust in response to the Pacific Plate subducting beneath the North American Plate. The thrust faults carried their respective thrust sheets up to 50 miles of displacement and the large folds have amplitudes of 5,000 to 10,000 feet.

Thrust faults and folds within the southeastern Idaho fold-thrust belt accommodated over 100 miles of horizontal shortening. These thrust faults are the bottom boundary of each thrust sheet of the same names which contain all of the passive margin sedimentary rocks above the fault. Each thrust sheet is 10,000 to 20,000 feet thick. Thrusting migrated in an eastward progression subsequently stacking the thrust sheets on top of each other. On the continental side of each of these imbricated thrust sheets, there becomes a structural foreland basin which receives sediment shed from the thrust sheet.

Chapter 1 introduces the Sevier-Laramide fold-thrust belt in Idaho-Wyoming and Utah. Chapter 2 presents a summary of structural deformation of the Idaho-Wyoming Overthrust Belt. Chapter 3 focuses on the East Central Idaho geology. Chapter 4 offers road logs through East Central Idaho from Salmon to Challis, Challis to Arco, and Mud Lake to Salmon.

• Format: Paperback
• Language: English
• ISBN: B0BXN8XJXB
• ISBN13: 9798386567071
• Release Date: March 2023
• Publisher: Independently Published
• Length: 216 Pages
• Weight: 0.65 lbs.
• Dimensions: 0.5" x 6.0" x 9.0"